<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button onclick="fun()">新增</button>
</body>
<script>
    //新增
    // function fun(){
    //     document.cookie = 'username=张三'
    // }
    // function fun(){
    //     document.cookie = 'username=张三;expires=' + new Date(2022, 10, 15, 01,32,10)
    // }

    function setCookie(cname, cvalue, exdays) {
        var d = new Date();
        d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
        var expires = "expires=" + d.toGMTString();
        document.cookie = cname + "=" + cvalue + "; " + expires;
    }
    function getCookie(cname) {
        var name = cname + "=";
        var ca = document.cookie.split(';');
        for (var i = 0; i < ca.length; i++) {
            var c = ca[i].trim();
            if (c.indexOf(name) == 0) { return c.substring(name.length, c.length); }
        }
        return "";
    }
    function checkCookie() {
        var user = getCookie("username");
        if (user != "") {
            alert("欢迎 " + user + " 再次访问");
        }
        else {
            user = prompt("请输入你的名字:", "");
            if (user != "" && user != null) {
                setCookie("username", user, 30);
            }
        }
    }

    window.onload = function () {
        checkCookie()
    }
</script>

</html>